Doctor home after round where he started (6)
I believe the answer is:
origin
'where he started' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'doctor home after round' is the wordplay.
I cannot quite understand how this works, but
'doctor' could be 'rig' (both can mean to forge or manipulate) and 'rig' is located in the answer.
'home' could be 'in' ('he's home' can mean 'he's in') and 'in' is present in the answer.
'round' could be 'o' (o is a circular letter) and 'o' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for origin that I've seen before include "Point of creation" , "Square one" , "Source, root" , "Source - provenance" , "Where one begins" .)